1. Field of the Invention
The present invention relates to a hard disc drive and, more particularly, to a hard disc drive utilizing a discrete type recording medium.
2. Description of the Prior Art
Research and development of a hard disc drive utilizing a discrete type recording medium, i.e., so-called discrete track media have been made recently. FIG. 1 of the accompanying drawings schematically shows a fragmentary enlarged plan view of one track of the discrete type recording medium. As shown in FIG. 1, a head positioning servo signal for the discrete type recording medium is shown, in which servo patterns 14 each made of a checkered pattern are recorded in advance on a recording medium 11 together with data recorded patterns 13, similarly to an optical recording medium, i.e., a so-called optical disc.
FIG. 2 shows a fragmentary enlarged cross-sectional view of a structure of the discrete type recording medium or disc. As shown in FIG. 2, concave and convex portions are formed on a disc substrate 11 due to the presence or absence of magnetic layer 12. More specifically, data recording patterns 13 each having concave and convex portions of relatively long cycle, to form a continuous data recording area i.e. long wavelength, and servo patterns 14 each having concave and convex portions of relatively short cycle, i.e., short wavelength, are formed on the disc substrate 11 in a mixed state.
The wavelength in this specification depicts a duration of cycle during which concave and convex portions, i.e., information patterns, are formed due to the presence or absence of the magnetic layer 12 on the discrete type recording medium 1, for example.
Considering the concave and convex portions formed by the presence or absence of the magnetic layer 12 as an undulation of a certain wave, as shown in FIG. 3, a floating amount of a floating slider 3 which is floated from the magnetic layer 12 could be considered as a fluctuation of the floating amount if the disc substrate 11 has an undulation. In FIG. 3, reference letter a represents the amplitude of the undulation, L the wavelength, H.sub.0 the minimum floating amount and .DELTA.h the fluctuated amount of the floating amount.
Assuming that a slider length L.sub.SL of the floating slider 3 is taken constant, then the fluctuated amount .DELTA.h of the floating amount is approximately expressed as shown in FIG. 4 of the accompanying drawings. Analysis of FIG. 4 reveals that the fluctuated amount .DELTA.h of the floating amount is changed by the undulation wavelength L (see Collection of Papers published by The Japan Society of Mechanical Engineers (edition C), Vol. 51, No. 469 (September 1985), pp. 2291 to 2299).
A study of FIG. 4 reveals that, when the undulation wavelength, namely, the wavelength L of the data recording pattern 13 and the servo pattern 14 is changed, the floating amount fluctuated amount .DELTA.h is changed, accordingly, the floating amount (H.sub.0 +.DELTA.h) of the floating slider 3 also is changed similarly. That is, above the same recording medium 1, the floating amount of the floating slider 3 is changed as h.sub.0 +.DELTA.h.sub.1, h.sub.0 +.DELTA.h.sub.2, . . . , for example, depending on the difference of length of the information pattern. Consequently, the distance (hereinafter referred to as "spacing amount") between a recording and/or reproducing head on the floating slider 3 and the magnetic layer 12 is fluctuated.
There is then the disadvantage such that a reproduced output voltage is lowered at the portion where the spacing amount is increased.
In order to avoid the fluctuation of the floating amount, as is clear from FIG. 4, it is proposed to reduce the floating amount fluctuated amount .DELTA.h by reducing the length L.sub.SL of the floating slider 3 as compared with the wavelength L of the information pattern. However, the shortest wavelength of the wavelength L of this information pattern, i.e., the wavelength of the servo pattern 14 is as small as less than about 1 .mu.m and a floating slider whose length is smaller than the above wavelength cannot be formed without difficulty.
Further, another technique is proposed, in which concave and convex portions comprising information patterns are filled and flattened after the magnetic layer 12 has been treated by the patterning process. In actual practice, a manufacturing process based on this technique is difficult and cumbersome, which unavoidably lowers the efficiency of mass production.